Method of making non-porous weld beads



United States Patent 3,378,669 METHOD OF MAKING NON-POROUS WELD BEADSAllan A. Dolomont, North Haven, Conn., assignor to Olin MathiesonChemical Corporation, a corporation of Virginia No Drawing. Continuationof application Ser. No. 339,853, Jan. 24, 1964. This application June30, 1967, Ser. No. 650,547

6 Claims. (Cl. 219-74) ABSTRACT OF THE DISCLOSURE This invention relatesgenerally to improvements in processing of aluminum welding wire, andmore particu lady to electrochemical treatment continuously applied toindefinite lengths of material to produce an aluminum welding wire whichyields a high quality nonporous weld bead when used in weldingcomponents of aluminum articles.

This is a continuation of application Ser. No. 339,853, filed Jan. 241964, and now abandoned.

One of the main deterrents to increased use of aluminum in highlystressed structures such as pressure vessels, missiles, etc., is theporosity found in welds made with the consumable electrode inert gasprocess and the non-consumable tungsten electrode inert gas process,more commonly known as the MIG and T16 processes. While the welding ofaluminum under these processes has progressed steadily in recent years,its more wide spread acceptance has been retarded by the presence ofporosity in the weld bead. In certain industrial applications wherestresses or pressures applied to the welded parts are not great, thepresence of porosity in the Weld bead may not present a major problem.However, in many of the volume markets such as those indicated above,porosity in the weld bead is not permitted, and where this defect ispresent, the component is rejected.

Porosity in welds are generally of two types: firstly, voids resultingfrom entrapment of the shielding gases or atmosphere within thesolidifying weld metal, and secondly voids caused by the release ofhydrogen from the solidifying weld metal. The first source can besubstantially reduced or completely eliminated by periodic checks onequipment and by making frequent control welds to establish that weldingprocedures are correct and uniform. This invention is directed towardthe elimination of porosity caused by the second source, i.e., formationof hydrogen bubbles within the weld bead.

These bubbles are caused by the introduction of hydrogen containingmaterials into the weld bead. During the welding these materials aredecomposed and the hydrogen so produced dissolves in the molten metal.Upon solidification, the lower solubility of the hydrogen in the solidmetal results in the rejection of hydrogen in solution and theproduction of small voids in the weld.

It has been found that hydrogen containing materials may enter the weldhead from a number of sources. The inert gases used in the welding areof such high purity that they can generally be discounted as a directsource of hydrogen. However, between the gas cylinder and the weldingare, atmospheric contamination may take place or water condensation mayoccur on the welding equipment. Preweld inspection can usually eliminatethese sources of hydrogen. A further source of hydrogen is contaminationof the are by the atmosphere mixing with the shielding gas. This can beeliminated by proper adjustment of the Welding parameters. Hydrogen mayalso enter the weld metal from the base plate; this source is "iceusually controlled by the metal manufacturer through proper castingfabrication techniques.

Thu-s, we have demonstrated that the welding wires themselves are themain uncontrollable source of hydrogen causing porosity in aluminumwelds. These wires are usually smaller than 0.125" in diameter and sohave a large ratio of surface area to volume. This means that the wiresurface or surface oxide can contribute considerable amounts of hydrogenfrom adsorbed, absorbed or hydrated water in the oxide. When the highrates of wire feed (up to 500" per minute) used in welding aluminum areconsidered, it can be readily appreciated that contamination of the wiresurface can be a major source of porosity.

It has become evident that there are two principal sources of hydrogencontaining materials on the surface of the welding wire. In theproduction of the wire, diameter rod is first drawn to 0.187 andsubsequently passed through an annealing furnace. Lubricants of aparticularly tenacious kin-d are used in drawing and are not usuallyremoved before annealing. In the annealing furnace the lubricants andtheir products of reaction are decomposed, thus leaving small carbonparticles adhering to the surface of the wire. Additional drawing tofinal gages causes the particles to be drawn into the surface of thewelding wire. conventionally, the wire is then degreased by knownmethods, packed and shipped. It has been found, however, that theconventional degreasing processes do not remove the carbon particles northe lubricant residues from the final draw. In subsequent storage thecarbon particles act as cathodic stimulators of corrosion acting ascathodes in small local galvanic cells. These allow aluminum in thepresence of moisture to act as an anode and produce an aluminumhydroxide or hydrous oxide film. It is the water in this film whichbreaks down in subsequent welding to produce free hydrogen whichproduces porosity upon freezing of the molten metal in the weld bead. Ithas also been found that even in the absence of the cathodic stimulatorsof corrosion, the oxide film normally on the wires can and does take upwater to produce a hydrous and hydrated oxide, particularly during longperiods of storage. Again, when the wires are used in welding the waterfrom the film is decomposed by the welding arc and forms relativelylarge amounts of free hydrogen which is readily taken up by the moltenweld metal. The freezing of the weld metal results in the rejection fromsolid solution of that quantity of by drogen which is above the solidsolubility of hydrogen in the particular alloy. This rejection ofhydrogen from solid solution results in weld metal porosity.

The removal of these lubricants is very difficult because, due to theircomplex nature, they cannot be removed by any one solvent. Whilechlorated hydrocarbons will generally remove petroleum type lubricants,they are not effective with the lard oil types which are used inconcentrations of up to 15 percent to improve the surface appearance ofdrawn wire. Alcohols or other solvents are required to remove thelatter. These methods, because of their complexity, are not economicallyfeasible for mass production of welding wires. They are also ineffectivein the removal of drawn-in carbon residue resulting from thedecomposition or cracking of the lubricants during intermediateannealing. As indicated above, this carbon residue is harmful in that itaccelerates corrosion and hydration of the wire oxide film upon exposureto humid atmospheres.

The removal of drawing lubricants and carbon residues, together with theoxide film and some base metal can be successfully accomplished byetching in solutions such as sodium hydroxide. While this method has metwith some degree of commercial acceptance, it has not found wide spreadfavor in view of the facts that the process is difficult to control andresults in an unsatisfactory surface appearance.

To obviate these and other disadvantages of prior art methods ofcleaning aluminum welding wire, We have provided an improved method ofhigh speed removal of lubricants from the surface of wires by passingthe wire, as part of .an electrical circuit, through an aqueous alkalineelectrolyte in which the wire is caused to be anodic. This results incomplete rapid and controllable degreasin-g of the wire so that onwelding no porosity is produced, the amount of weld spatter is greatlyreduced and the appearance of the surface of the weld bead is greatlyimproved.

Accordingly, it is a prime object of the present invention to provide amethod of treating continuously moving aluminum welding wire such thatwelds made therefrom will be free of objectionable porosity.

It is another object of the present invention to provide a method oftreating continuously moving aluminum welding wire in which the wire isrendered completely free of deleterious contaminants which produceobjectionable porosity in the weld metal.

It is still another object of the present invention to provide a processfor treating continuously moving aluminum welding wire which completelyremoves the hydrogen containing materials normally present inconventionally produced wire which materials result in hydrogen formedbubbles in the weld metal.

It is still another object of the present invention to provide a processfor treating continuously moving aluminum welding wire which provides avery thin and uniform film on the wire surface to resist hydration andminimize corrosion or adsorption of water.

These and other objects of the present invention will become moreapparent from a consideration of the following detailed description.

In one of its broader aspects, the objects of this invention areachieved by immersing the wire in a first aqueous alkaline solutioncontaining an anode strip, continuously immersing the wire in a secondaqueous alkaline solution containing a cathode strip, passing anelectric current through the electrolytes while the wire is immersedtherein, rinsing the wire in cold water, immersing the wire in apassivating and neutralizing acid bath, again rinsing the wire in coldwater and finally drying and coiling the wire.

The process of this invention is directed principally toward improvingthe welding characteristics of several groups of aluminum alloy weldingwires. One of these is the aluminum-iron-silicon group which containsaluminum ranging from 99.30% to 99.99%, balance impurities normal forthis group, of which the 1000 and 1100 series of alloys arerepresentative. Another group is the 2000 series of alloys whichcontains from 3% to 7% copper, 0.1% to 0.5% manganese, .05 to 0.5%titanium with balance aluminum plus impurities normal for this group.Another group to which this invention is applicable is the 4000 seriescontaining from 3% to 14% silicon, either with or without 3% to 6%copper, with the balance aluminum plus normal impurities. Still anothergroup is the 5000 series containing from 2% to 7% magnesium, with thebalance aluminum plus normal impurities.

In accordance with the practice of this invention, a supply of weldingwire suitably coiled on a spool is mounted upon suitable processingapparatus in a manner to facilitate its being unwound from the supplyspool and continuously drawn through the apparatus, to be there afterrewound on a take up spool all in a manner well known in the art. Thewire is guided by any suitable means from the take oft spool and into afirst tank containing an aqueous alkaline solution which contains ananode strip, and is thereafter guided out of this tank, across aninsulating gap, and into a second tank containing a similar solutionhaving a cathode strip. This arrangement facilitates an electric circuitconsisting of the anode strip, the first alkaline solution, the wire,the second alkaline solution and the cathode strip. By this arrangementthe wire is made a part of the circuit without having to mechanicallycontact the wire or provide any type of rubbing contact which might tendto mar or otherwise injure the appearance of the finished wire.

It should be noted, however, that within the limitations imposed bymechanical contact of an electrode with the wire, it is possible toaccomplish the objects of the invention by utilizing a single tank foranodic treatment of the wire in an aqueous alkaline solution. Thismethod is less desirable than the double tank solution contacting methodbecause of mechanical contact of electrode and moving wire with highcurrent passage which usually leads to arcing and marking of the wire.

In order to achieve the desired cleaning effects on the wire surface,the alkaline baths through which the wire is passed are adjusted to havea titratable alkalinity ranging from that produced by 1% to 40% NaOHwith an optimum value of approximately 10%, and a pH greater than 10.The solutions are generally prepared from any one, or a combination ofseveral, of the compounds selected from one of two groups, either thealkali metal hydroxides and ammonium ion, or any alkali metal salt of astrong base and weak acid which hydrolyzes to an alkaline solution.Examples of the first group are hydroxides of sodium, potassium,lithium, rubidium, cesium and ammonium. Examples of the second group aresodium, potassium, lithium, rubidium and cesium salts of carbonates,phosphates and phosphites including polyphosphates and polyphosphites,and cyanides. It is, of course, possible to use mixtures of sodiumhydroxide and other bydroxides as well as mixtures of hydroxides andalkali salts, in particular phosphates. A preferred alkaline electrolytehas been found to be an aqueous solution of from 3% to 15% sodiumhydroxide with the balance water and preferably a solution of about 10%has been found to achieve excellent results when other variables as setforth hereinafter have been properly adjusted.

It may be desirable in some situations to include certain additives inthe alkaline solutions for specific purposes. For example, wettingagents may be added which increase the rate of oil removal. Such wettingagents must, of course, be stable in the solutions used. Also, chelatingagents such as EDTA (ethylenediaminetetra acetic acid) or its sodiumsalt, or sugar acids such as gluconic acid, may be added to prevent theformation of hard scale on tanks and heating coils.

The alkaline baths are generally maintained at a temperature rangingfrom room temperature to the boiling point of water, more commonlywithin the range of about 40 to centigrade and optimally at about 65centigrade. The temperature and concentration of the alkaline bath aregenerally adjusted to achieve a desired rate of metal removal in theelectroetching process which takes place in the first tank. Since it isdesirable to maintain metal removal as low as possible and still achievean effective cleaning action, both alkaline concentration andtemperature are adjusted to fairly low values in comparison to normaletching procedures.

While a resident immersion time ranging from 2 to seconds has been foundto be operable in achieving a desirable cleaning effect on the wire, animmersion time of 6 seconds with afairly dilute solution and lowoperating temperature facilitates the arrangement of an efficient andhigh production capacity apparatus for performing the process of thisinvention.

With regard to current density at the anodically treated wire surface,depending upon the variables mentioned above, the current density mayrange 25 to 1000 amps per square foot and a voltage of between 7 to 20depending upon the distance between the electrodes, the concentration ofelectrolyte, and the operating temperature.

As the wire passes through the first and second tanks, whichrespectively have anode and cathode strips in the electric circuit, thewire becomes cathode in the first tank and anode in the second tank.This causes, upon the application of power, a strong gas evolution atthe wire in the first tank. This gas evolution has a scrubbing action onthe wire which assists in the removal of the drawing lubricants andharmful residues. The gas evolution is caused by the electrolyticreduction of hydrogen to form gas bubbles which result in the scrubbingaction. The electrolytic action also, to some extent, protects thealuminum against dissolution in the alkaline solution However, somealuminum from the wire goes into solution, the amount depending onconcentration, temperature and current density. Thus, a mild etching isalso produced in this first tank. The extent of etching, as indicatedabove can be controlled by controlling the time in solution and theconcentration of the alkaline solution, or the extent of current densityapplied to the circuit. The etching action together with the gasscrubbing completely removes the drawing lubricants, oxide film, andharmful residues.

As the now cleaned wire passes from the first tank to the second tank,its polarity is changed and the wire becomes anode in the second tank.In the second tank the wire is subjected to a mild electropolishingaction which removes any hydrogen which may have entered the metal fromthe cathodic treatment in the first tank. Also, the positive charge inthe wire repels any positively charged particles of dirt which may stilladhere to the wire surface, together with any oxidizable impurities suchas metal deposits. In the second tank the current density must besufficiently high to effect an electropolishing action which deposits athin oxide film on the surface of the wire to protect the wire againstany subsequent hydration during periods of extensive storage prior touse. If the current density is not sufficiently high, the wire will besubjected to an electroetching effect which results in uneven metalremoval with a consequent undesirable appearance. After emerging fromthe second tank, the resultant wire surface is very smooth and shiny inappearance and is exceptionally clean and free of contaminants whichwould otherwise have a deleterious effect upon the weld bead.

With regard to the passivating and neutralizing acid bath through whichthe wire passes after emerging from a cold water rinse following theanodic electrolytic bath, it has been found that a nitric, hydrofluoricor chromic acid solu tion having concentrations of these acids in therange of 2 to 70 percent, are suitable for removing smut, and toneutralize any residue or hydroxide solution or other residue which maystill be adhering to the Wire surface. The acid bath may be limited toas short a time as necessary, usually a few seconds, to remove theaforementioned metal or hydroxide residue.

Subsequent to the acid bath, the wire is passed through a second coldwater rinse, after which it is dried by a conventional hot air blowingapparatus and recoiled on a suitable spool.

Aluminum welding wire treated by the above described electrocleaningmethod results in welds that are found to be completely free ofporosity. The uniformity of the surface of the wire extends weldingcontact tube life and results in a welded are that is very stable, Theweld bead is very smooth and free of the dark smut that is present whenconventionally cleaned wires are used. It has been found that spatterthat is generally disposed along the weld bead is also reduced. Of majorimportance to the achievement of a porosity free weld is the fact thatinert gas welding wire cleaned by the process discussed here is far lesssusceptible to hydration and/or corrosion in humid atmospheres thanuncleaned or conventionally cleaned wire. Thus, it has been found thatafter exposure to high humidity atmospheres in the order of 98 percentrelative humidity at a 100 F. for 60 days, electrocleaned wire stillproduces acceptable welds whereas uncleaned or conventionally cleanedwire presents porous welds after even shorter exposures.

The following are specific examples of the practice of this inventionand are to be deemed purely illustrative and not all inclusive.

Example I A sample of aluminum welding wire fabricated from alloy 5356was continuously immersed in an aqueous solution of 10 percent sodiumhydroxide at 65 Centigrade in a first tank containing an anode strip,was withdrawn from this tank and immersed in a second aqueous solutionof 5 percent sodium hydroxide maintained at 65 centigrade in a secondtank containing a cathodic strip. A current density of 950 amps persquare foot at 11 volts was applied to the anode. The wire passedthrough the alkaline solutions, then through a water rinse, a nitricacid rinse, a second water rinse, and a drying and coiling operation ata rate of 40 feet per minute with a resident time of 7 seconds in eachof the alkaline baths. The dried and coiled wire was then stored for 30days in an atmosphere of percent relative humidity at F. After weldingwith this wire careful X-ray inspection of the weld bead showed nodetectable porosity.

Example II A sample of aluminum welding wire fabricated from alloy 4043was continuously immersed in an aqueous solution of 10 percent sodiumhydroxide at 65 centigrade in a first tank containing an anode strip,was withdrawn from this tank and immersed in a second aqueous solutionof 5 percent sodium hydroxide maintained at 65 centigrade in a secondtank containing a cathodic strip. A current density of 950 amps persquare foot at 11 volts was applied to the anode. The wire was passedthrough the alkaline solutions, then through a water rinse, a nitric andhydro fluoric acid rinse, a second water rinse, and a drying and coilingoperation at a rate of 40 feet per minute with a resident time of 7seconds in each of the alkaline baths. The dried and coiled wire wasthen stored for 30 days in an atmosphere of 95 percent relative humidityat 100 F, After welding with this Wire careful X-ray inspection of theweld bead showed no detectable porosity.

Example III rinse, a nitric acid rinse, a second Water rinse, and adrying and coiling operation at a rate of 50 feet per minute with aresident time of 5 seconds in each of the alkaline baths. The dried andcoiled wire was then stored for 30 days in an atmosphere of 95 percentrelative humidity at 100 F. After welding with this wire careful X-rayinspection of the weld bead showed no detectable porosity.

Example IV A sample of aluminum welding wire fabricated from alloy 1100was continuously immersed in an aqueous solution of 10 percent sodiumhydroxide at 65 centigrade in a first tank containing an anode strip,was withdrawn from this tank and immersed in a second aqueous solutionof 5 percent sodium hydroxide maintained at 65 centigrade in a secondtank containing a cathodic strip. A current density of 950 amps persquare foot at 11 volts was applied to the anode. The wire was passedthrough the alkaline solutions, then through a water rinse, a nitricacid rinse, a second water rinse, and a drying and coiling operation ata rate of 30 feet per minute with a resident time of 7 seconds in eachof the alkaline baths. The dried and coiled wire was then stored for 30days in an atmosphere of 95 percent relative humidity at 100 F. Afterwelding with this wire careful X-ray inspection of the weld bead showedno detectable porosity.

It will be apparent from the foregoing description that there has beenprovided a method of treating aluminum welding wire which provides asolution to the foregoing problems and achieves the aforementionedobjects. It is to be understood that the invention is not limited to theexamples described herein which are deemed to be merely illustrative ofthe best modes of carrying out the invention, but rather is intended toencompass all such modifications as are within the spirit and scope ofthe invention as set forth in the appended claims.

What I claim and desire to secure by Letters Patent 1s:

1. A method of making a high quality non-porous weld bead comprising thesteps of (A) providing an indefinite length of continuously movingaluminum welding wire,

(B) continuously passing said wire through a first aqueous alkalinesolution containing an anode electrode, said anode being spaced fromsaid wire by said first solution,

(C) continuously passing said wire through a second aqueous alkalinesolution containing a cathode electrode, said cathode being spaced fromsaid wire by said second solution, said first and second solutionshaving a titratable alkalinity equivalent to sodium hydroxide solutionsranging from 1 to 40%,

(D) applying an electric current to said electrodes as said wire passesthrough said solutions whereby said wire is cathodic in said firstsolution and anodic in said second solution,

(B) rinsing said wire,

(F) passing said wire through a passivating and neutralizing acid bath,

(G) rinsing said wire,

(H) drying said wire, and

(I) welding with said wire to provide a high quality,

non-porous weld bead.

2. The method of claim 1 wherein said first and second solutions areaqueous alkaline solutions of a compound selected from the groupconsisting of alkali metal hydroxides, ammonium hydroxide, alkali metalsalts of a strong base and weak acid which hydrolyze to an alkalinesolution, and mixtures thereof, said solutions having a pH of over 10.

3. The method of claim 1 wherein said alkaline solutions are maintainedat a temperature within the range of 40 to 80 C.

4. The method of claim 1 wherein said current density is within therange of 25 to 1000 amps/sq. ft.

5. A method of making a high quality non-porous weld bead comprising thesteps of (A) providing an indefinite length of continuously movingaluminum welding wire,

(B) continuously passing said wire through a first aqueous alkalinesolution containing an anode electrode, said anode being spaced fromsaid wire by said first solution,

(C) continuously passing said wire through a second aqueous alkalinesolution containing a cathode electrode, said cathode being spaced fromsaid wire by said second solution, said first and second solutionshaving a titratable alkalinity equivalent to sodium hydroxide solutionsranging from 1 to 40%,

(D) applying an electric current to said electrode as said wire passesthrough said solutions whereby said wire is cathodic in said firstsolution and anodic in said second solution, wherein the total residencetime in said first and second solutions is from 2 seconds to seconds,

( E) rinsing said wire,

(F) passing said wire through a passivating and neutralizing acid bath,

(G) rinsing said wire, and

(H) welding with said wire to provide a high quality,

non-porous weld head.

6. A method of making a high quality non-porous weld bead comprising thesteps of (A) providing an indefinite length of continuously movingaluminum welding wire,

(B) continuously passing said wire through a first aqueous alkalinesolution containing an anode electrode, said anode being spaced fromsaid wire by said first solution,

(C) continuously passing said wire through a second aqueous alkalinesolution containing a cathode electrode, said cathode being spaced fromsaid wire by said second solution, said first and second solutionshaving a titratable alkalinity equivalent to sodium hydroxide solutionsranging from 1 to 40%,

(D) applying an electric current to said electrodes as said wire passesthrough said solutions whereby said wire is cathodic in said firstsolution and anodic in said second solution, wherein the total residencetime in said first and second solutions is from 2 seconds to 120seconds,

(E) rinsing said wire, and

(F) welding with said wire to provide a high quality,

non-porous weld bead.

References Cited UNITED STATES PATENTS 1,068,411 7/ 1913 Chubb 204-281,946,150 2/ 1934 Tosterud 204-5 8 2,096,309 10/ 1937 Pullen 204-582,376,082 5/1945 Pullen 204-29 2,671,717 3/ 1954 Furguson 204-332,681,402 6/ 4 Muller 117-202 HOWARD S. WILLIAMS, Primary Examiner. T.TUFARIELLO, Assistant Examiner.

